1. Field of the Invention
This invention relates to a disposable syringe with automatically retractable hypodermic needle, for use in the injection of medicinal substances and/or the removal of samples of blood and liquids in general in human or veterinary medicine, with the special feature that once the operation is performed the application of slight additional pressure to the end of the piston's travel causes the needle to be automatically shot inwards, with it remaining permanently housed in the interior in order to protect the operator from pricks or contact with pathogenic substances, and also making it unusable for subsequent applications.
2. Description of the Related Art
In the procedures mentioned hypodermic needles are normally fitted to syringes and represent a great hazard of infection to those persons responsible for their subsequent handling, not only because of their ability to prick, but also because they retain contaminating residues. In order to protect operating personnel from these risks, in practice containers are used which are designed to capture and store these units, which are then transported to incinerators for total destruction. However these operations are risky because disposal does not take place immediately, especially in operating theaters in which the operating surgeon's attention is concentrated on the operating field, and little attention is involuntarily paid to the disposal of such units once used. On the other hand, those responsible for removing the containers mentioned are exposed to accidents given that the uncovered needles can pass through their walls and the operation of placing them in a protective cap represents an additional risk.
There is also the possibility that someone committing a fraudulent act might reuse the syringes disposed of, causing severe harm to subsequent patients.
Various types of hypodermic syringes with a retractable needle which are intended to overcome the disadvantages described, which have a functional behavior which differs from that described herein, are known. Nevertheless those which are most widely known will be mentioned above, pointing out their obvious differences.
These are U.S Pat. Nos. 5,152,750, 5,180,370, 5,222,944, 5,382,235, 5,578,015 and 5,616,134, which form a group with nonautomatic retraction. U.S. Pat. No. 5,190,526, which requires great complexity in fitting of the piston, given that this must disassemble, in order to break, into a plug which is retained at the working front and a retracting capture unit, with the disadvantage that there is no possibility of fitting and removing the needle from the exterior, nor of retaining the residual liquids which normally remain at said front; on the other hand the needle used has to be manufactured specially only for this mechanism. U.S. Pat. No. 5,324,265, which is merely an improvement on the above, which converts it into a syringe with an externally removable needle, but retains the other disadvantages mentioned. U.S. Pat. No. 5,320,606, in which the member acting as a piston slides externally until its edge produces an opening for a seal which holds the needle-holding tip in position, which is integral with an elastomer member which controls the passage of liquids; the elastic condition required of this tubular member represents a construction problem in the region in which it is incorporated with the needle holder and, at its other end, with the end of the tube containing it; furthermore, the positioning of the fin for fixing this syringe, which is so close to its working front, makes it inconvenient to handle. U.S. Pat. No. 5,656,031, which has a breaking and retraction mechanism initiated by the pusher of an external protector, which gives rise to risks in application and our U.S. application Ser. No. 09/005681, which is fundamentally distinguished by the manner in which it captures the needle and its capturing mechanism, which does not permit the option of external mounting.